Project Summary Alcohol misuse (e.g., binge drinking) in mid-adulthood and its negative consequences, including alcohol use disorder (AUD) are prevalent, increasing, and expensive. In the last decade, high risk drinking increased 37% and AUD 47% among 30-44 year olds (and even more at older ages). Excessive drinking cost the U.S. $249 billion and is among the leading preventable causes of death in this country. Psychiatric comorbidity is the rule rather than the exception among problem drinkers, particularly after age 30. Given the trajectory of this societal burden, NIAAA has prioritized a developmental approach to the identification of mechanisms underlying alcohol misuse and problems and co-occurring mental health conditions across the lifespan (Goals 1-2, Objective 1a). The Pittsburgh ADHD Longitudinal Study (PALS) was designed to prospectively study the onset, course, and causes of AUD in a large cohort of children at risk for alcohol problems---those diagnosed with one of the most prevalent childhood psychiatric disorders, Attention-Deficit/Hyperactivity Disorder (ADHD). ADHD predicts early onset (adolescent) alcohol use, increased alcohol-related problems, and AUD in emerging adulthood but mechanisms of alcohol problem risk into mid-adulthood are unknown. Moreover, ADHD complicates AUD treatment (e.g., relapse rates are much higher). Research on adult ADHD has exploded, but amply powered longitudinal studies of childhood ADHD into mid-adulthood, when drinking problems become entrenched and mediating variables have recently been shown to change, are absent from the literature and are now even more crucial given the proliferation, and limitations, of cross-sectional studies of adult ADHD and AUD. Moreover, data are needed on the dynamic nature of within-person, daily risk processes not captured in traditional infrequent assessments (e.g., daily fluctuations in, and effects of, impulsivity and mood on alcohol use as a function of context) that may be unique and incrementally informative for individuals with ADHD. The PALS is a well-characterized, well-retained (>90% retention) sample (365 ADHD, 227 nonADHD) prospectively studied from childhood to age 29 with ongoing age-targeted assessments; age 35 assessments are partially collected. We propose a novel continuation of our cohort-sequential design to age 39 that includes an embedded 17-day ecological momentary assessment (EMA) at age 37 to assess short- and long-term within-person developmental pathways from childhood ADHD to mid-adulthood alcohol problems. The PALS has the capacity to test pathways to alcohol problems (including negative affect-related) that are more likely to emerge in older adulthood. Findings have the potential to identify novel and malleable contributors to mid-adulthood AUD and inform intervention opportunities for a prevalent, intractable comorbidity.